This is vintage Chesterton. Funny, Thought provoking, whimsical... I've read it and loved it. I found a great description on line and will post it here...

The Man Who Was Thursday by G. K. Chesterton

A WILD, MAD, HILARIOUS AND PROFOUNDLY MOVING TALE

It is very difficult to classify THE MAN WHO WAS THURSDAY. It is possible to say that it is a gripping adventure story of murderous criminals and brilliant policemen; but it was to be expected that the author of the Father Brown stories should tell a detective story like no-one else. On this level, therefore, THE MAN WHO WAS THURSDAY succeeds superbly; if nothing else, it is a magnificent tour-de-force of suspense-writing.
However, the reader will soon discover that it is much more than that. Carried along on the boisterous rush of the narrative by Chesterton's wonderful high-spirited style, he will soon see that he is being carried into much deeper waters than he had planned on; and the totally unforeseeable denouement will prove for the modern reader, as it has for thousands of others since 1908 when the book was first published, an inevitable and moving experience, as the investigators finally discover who Sunday is.

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